An account name is asked for, why is my entry is not recognized?

After logging in an user name is asked for. A-Z, a-z, 0-9. When entering jim.m420 nothing happens. Why is there no response?

User names and passwords are verified by the code of the software package you are trying to log into. How they work (or don't work in your case) depends on a set of rules. For example is the decimal between the two "m' characters allowed? Is the login case sensitive?

Your entry is not recognized because what you entered does not match what the system is expecting. To provide a more specific answer would require knowing what software you're asking about.